Lansoprazole is a proton pump inhibitor that reduces gastric acid secretion in a dose-dependent manner via inhibition of H+/K+-adenosine triphosphatase in gastric parietal cells. It also exhibits antibacterial activity against Helicobacter pylori in vitro. During almost 10 years of clinical use, lansoprazole has proved effective and well tolerated in a wide range of acid-related disorders, including gastro-oesophageal reflux disease (GORD), duodenal ulcers, gastric ulcers, non-steroidal anti-inflammatory drug-related ulcers, as well as non-ulcer dyspepsia and acid hypersecretion. It is also used, in combination with antibiotics, for H. pylori eradication. In the above indications, lansoprazole has generally proved to be superior to the histamine H2-receptor antagonists, and is at least as effective as the other currently available proton pump inhibitors. This review aims to evaluate the pharmacology, efficacy, safety and cost-effectiveness of lansoprazole in acid-related disorders, with particular emphasis on its use in GORD and H. pylori eradication regimens.